Overproduction of cytokines such as IL-1 and TNF-α is implicated in a wide variety of inflammatory diseases, including rheumatoid arthritis (RA), psoriasis, multiple sclerosis, inflammatory bowel disease, endotoxin shock, osteoporosis, Alzheimer's disease, and congestive heart failure, among others. [See Henry et al., Drugs Fut., 24:1345-1354 (1999), and Salituro et al., Curr. Med. Chem., 6:807-823 (1999)]. There is convincing evidence in human patients that protein antagonists of cytokines, such as, for example, monoclonal antibody to TNF-α (Enbrel) [Rankin et al., Br. J. Rheumatol., 34:334-342 (1995)], soluble TNF-α receptor-Fc fusion protein (Etanercept) [Moreland et al., Ann. Intern. Med., 130:478-486 (1999)], and/or IL-1 receptor antagonist [Bresnihan et al., Arthritis Rheum., 41:2196-2204 (1998)], can provide effective treatment for chronic inflammatory diseases. As none of the current treatments for inflammatory diseases provides complete relief of symptoms, and as most current treatments are associated with various drawbacks such as side effects, improved methods for treating inflammatory diseases are desirable.
TNF-α is a protein whose synthesis occurs in many cell types in response to an external stimulus, such as, for example, a mitogen, an infectious organism, or trauma. Signaling from the cell surface to the nucleus proceeds via several intracellular mediators including kinases that catalyze phosphorylation of proteins downstream in the signaling cascade. Important mediators for the production of TNF-α cytokine are the mitogen-activated protein (MAP) kinases, and in particular, p38 kinase.
p38 Kinases are activated in response to various stress stimuli, including, but not limited to, proinflammatory cytokines, endotoxin, ultraviolet light, and osmotic shock. Activation of p38 requires dual phosphorylation by upstream MAP kinase kinases (MKK3 and MKK6) on threonine and tyrosine within a Thr-Gly-Tyr motif, characteristic of p38 isozymes.
Four iso-forms of p38 have been described. The α and β forms are expressed in inflammatory cells and are thought to be key mediators of TNF-α production. Inhibition of the enzymes p38α and β in cells results in reduced levels of expression of TNF-α, and such inhibitors are effective in animal models of inflammatory disease.
Molecular cloning of human p38α identified two isozymes, which are the splice variant product of a single gene. Three additional gene products have subsequently been identified, p38β, p38γ, and p38δ. p38 kinases phosphorylate and activate the transcription factors, ATF-2, MAX, CHOP, and C/ERPb, suggesting a role of p38 kinases in gene regulation. In addition, p38 kinases phosphorylate other protein kinases, such as MAPK activated protein kinase-2/3 (MAPKAP-K2/3, or MK2/3), and MAP-kinase-interacting kinase 1/2 (MNK1/2). Recently, activation of MK2 has been shown to be essential for LPS-induced TNF-α expression [Kotlyarov et al., Nature Cell Biol., 1:94-97 (1999)]. Mice lacking MK2 exhibit a 90% reduction in the production of TNF-α and are resistant to shock induced by LPS. The reduction in TNF-α amounts is due not to decreased production of the TNF-α mRNA, but rather to diminished production of the TNF-α protein, suggesting that MK2 regulates biosynthesis of TNF-α at a post-transcriptional level.
Ample evidence indicates that the p38 pathway serves an important role in inflammatory process mediated by IL-1 and TNF-α.
Small molecule inhibitors of p38 are expected to have several advantages over protein inhibitors of TNF-α or IL-1. p38 inhibitors not only block the production of TNF-α and IL-1, but also directly interfere with many of their secondary biological effects. In addition, small molecule inhibitors are unlikely to induce immune reaction in patients, and are believed active following oral administration.
The present invention provides novel compounds that are potent and selective inhibitors of p38α and β, and as such, are also potent inhibitors of TNF-α expression in human cells. Compounds of the present invention are useful in the treatment of p38- and TNF-α expression-mediated inflammatory and other disorders, including, but not limited to, bone resorption, graft vs. host reaction, atherosclerosis, arthritis, osteoarthritis, rheumatoid arthritis, gout, psoriasis, topical inflammatory disease states, adult respiratory distress syndrome, asthma, chronic pulmonary inflammatory disease, cardiac reperfusion injury, renal reperfusion injury, thrombus, glomerulonephritis, Chrohn's disease, ulcerative colitis, inflammatory bowel disease, multiple sclerosis, endotoxin shock, osteoporosis, Alzheimer's disease, congestive heart failure and cachexia.